The use of cellular telephones has become widespread in recent years. The convenience of carrying such telephones on one's person has increased due to improvements in the size, shape, and weight of such phones, and the growing need of people in the business community to be continuously accessible to clients and co-workers has further contributed to the increased use of cellular phones.
Most cellular phones in use today employ a rechargeable direct current power source for powering a circuit which controls the functioning of the phone. While the rechargeability of the power source often provides economic advantages in the long term as compared to a nonrechargeable power source, the typical life cycle of a rechargeable battery (i.e. the period between rechargings) tends to be somewhat shorter than that of most nonrechargeable batteries. In fact, for many users of cellular phones, recharging the power source is a frequent task which may require several continuous hours of non-use. These significant non-use periods pose a potential danger for those who rely upon a cellular phone to be operable in emergency or other critical situations. Thus, both rechargeable and nonrechargeable power sources have advantageous features lacking in other power sources. More generally, certain types of power sources have advantages and disadvantages with respect to other types of power sources, particularly with regard to issues of life span, rechargeability, size, shape, and weight of the power sources.